A study of the field gradients at 39K nuclei surrounding a substituted Na+ ion in a single crystal of KF by nuclear magnetic pulsed double resonance

A high-sensitivity nuclear magnetic pulsed double-resonance technique is described. The method has been used to determine the quadrupole interactions of 39K nuclei at (1, 1, 0) and (2, 0, 0) lattice sites relative to a substituted Na+ impurity at (0, 0, 0) in a single crystal of potassium fluoride. The values obtained for the largest principal value of the field gradient tensor are |Vz'z’| = 0.163 x 10 14 e. s. u. for the (2, 0, 0) site, and |Vz'z’| = 0.131 x 1014 e. s. u. for the (1, 1, 0) site, with an asymetry parameter ŋ = 0.607. These values have been compared with those calculated for a simple ionic model introduced by Das & Dick (1962). In this treatment the maximum number of ions surrounding the impurity which have been allowed to relax is 896. The best overall agreement with experiment occurs when the shell model modification of Dick(1966) to the Tessman, Kahn & Shockley (1953) ionic polarizabilities is chosen. In this case the calculated values are: for the (2, 0, 0) sites |VZ'Z'| = 0.097 x 1014 e. s. u., and for the (1, 1, 0) sites |Vz'z’| = 0.106 x 1014 e. s. u. and ŋ = 0.176.